firstDayOfWeek

    private func firstDayOfWeek(date:Date) -> Date {
        let cal = Calendar.current
        let firstWeekDay = cal.firstWeekday
        let thisWeekDay = cal.dateComponents([.weekday], from: date).weekday!
        var diff = thisWeekDay - firstWeekDay
        if thisWeekDay < firstWeekDay {
            diff += cal.weekdaySymbols.count
        }
        diff = -1 * diff
        let firstDay = cal.date(byAdding: .day, value: diff, to: date)!
        return firstDay
    }